The present invention relates to the transcatheter delivery and remote deployment of implantable medical devices and more particularly implantable intraluminal devices of either the self-expanding type or the balloon expandable type.
Endoluminal therapies typically involve the insertion of a delivery catheter that transports an implantable prosthetic device into the vasculature through a small, often percutaneous, access site in a remote vessel. Once access to the vasculature is achieved, the delivery catheter is used to mediate intraluminal delivery and subsequent deployment of the prosthesis via one of several techniques. In this fashion, the prosthesis can be remotely implanted to achieve a therapeutic outcome. In contrast to conventional surgical therapies, endoluminal treatments are distinguished by their xe2x80x9cminimally invasivexe2x80x9d nature.
Self-expanding endoprostheses are generally comprised of a stent component with or without a graft covering over the stent interstices. They are designed to spontaneous dilate (i.e., elastically recover) from their delivery diameter, through a range of intermediary diameters, up to a maximal, pre-determined functional diameter. The endoluminal delivery and deployment of self-expanding endoprostheses pose several unique problems. First, the endoprosthesis itself must be radially compacted to a suitable introductory size (or delivery diameter) to allow insertion into the vasculature, then it must be constrained in that compacted state and mounted onto a delivery device such as a catheter shaft. Subsequently, the constraint must be removed in order to allow the endoprosthesis to expand to its functional diameter and achieve the desired therapeutic outcome. Preferably, the means of constraint will not adversely affect the delivery catheter performance (e.g., detracting from the flexibility of the delivery system) or add significantly to introductory profile. The constraint must also incorporate some type of release mechanism or scheme that can be remotely actuated by the implanting clinician. Consequently, deployment methodologies that are consistent with conventional interventional practices are preferred.
Delivery mechanisms for self-expanding endoprostheses of the prior art may be generally classified into one of two general categories, either coaxial sheaths or fiber-based constraints. Delivery systems also exist that use both of these types of mechanisms.
Tubular coaxial sheaths are one approach used to constrain the compacted self-expanding endoprosthesis. Normally, these coaxial sheaths extend over the entire length of an inner delivery catheter onto which the endoprosthesis is mounted near the catheter tip (i.e., leading end). Deployment is typically initiated by pulling on a handle or knob located near the hub (i.e., trailing end) of the catheter, which retracts the constraining sheath and allows the device to expand. During this procedure, the clinician maintains the position of the device by holding the inner (delivery) catheter in a stationary position. Existing problems and/or complications with the tubular coaxial sheath type of delivery system include friction between compacted device and constraining sheath, friction between the constraining sheath and delivery catheter, and friction between the delivery catheter and constraining sheath hemostasis valve, all of which can hinder deployment accuracy, speed and control. Additionally, a tubular coaxial constraining sheath can also reduce flexibility and add introductory profile due to the thickness of the constraining sheath.
U.S. Pat. No. 6,086,610 to Duerig et al. teaches a self-expanding stent provided with a tubular constraining sheath that is plastically deformable by a circumferential distending force such as a catheter balloon. This sheath remains implanted with the stent following deployment and fully covers the entire circumference of the stent in the fashion of a conventional stent covering, i.e., the tubular sheath is not disrupted. The Duerig et al. device is delivered from a conventional balloon catheter, but thought to have limitations, including radial recoil of the sheath after the balloon is pressurized, which can compromise luminal gain. Further, the presence of the cover may adversely affect the ability of the stent to fully deploy, and the balloon length must be equal to or longer than the stent, and this long balloon can potentially damage the vessel.
In the fiber-based delivery systems, the self-expanding endoprosthesis is constrained in the delivery profile by one or more removable fibrous strands, with or without an additional implantable constraint element. The endoprosthesis is released from its compacted state through tension applied to a deployment xe2x80x9ccordxe2x80x9d that normally runs through an additional lumen within the delivery catheter. Typically, applying tension to the deployment cord initiates the release of the fiber constraint by unlacing linear slip knots (e.g., Lau, et al., U.S. Pat. No. 5,919,225), removing circumferential croquet knots (e.g., Strecker, U.S. Pat. No. 5,405,378), or detaching the interlocking loops of a warp-knitted constraint (e.g., Armstrong et al., WO99/65420). Other fiber-based delivery systems are described by Lindemann, U.S. Pat. No. 4,878,906, and Hillstead, U.S. Pat. No. 5,019,085.
Another variant of the fiber-based delivery systems is the mechanism employed in the EXCLUDER(copyright) endoprosthesis marketed by W. L. Gore and Associates, Inc (Flagstaff, Ariz.). This mechanism entails a xe2x80x9cchain-stitchxe2x80x9d sewn into the seam of a biocompatible constraining tube that contains the compacted endoprosthesis. Applying tension to the fibrous constraint in this mechanism allows the seam in the biocompatible constraining tube to be open, and the self-expanding endoprosthesis to deploy. The biocompatible constraining tube is implanted along with the endoprosthesis, trapped between the abluminal surface of the device and the wall of the host vessel. See WO98/27894.
U.S. Pat. Nos. 5,755,769 and 6,019,787 to Richard et al. teach another constraining sheath around a self-expanding stent. The sheath is cut longitudinally into several segments by cutting wires or fibers actuated by pulling a handle at the opposite end of the delivery system. The sheath is attached to or integral to the delivery catheter with the result that the segments are removed with the catheter following stent deployment. No catheter balloon or other means for exerting a circumferential disrupting force to the sheath is suggested, nor are materials appropriate for the sheath suggested. This design requires lines to run over the length of the catheter.
Problems with fiber-based type of delivery systems include possible premature deployment during introduction to the vascular system through hemostasis valves, extra lumens required on the delivery catheter which can increase profile, possible snagging of fiber(s) on the compacted implantable device, the possibility of emboli resulting from moving lines between the catheter and the blood vessel, and possible breakage of the deployment cord itself.
The present invention relates to a constraining sheath for use around an endoprosthesis (e.g., a stent device, with or without a graft covering), which may be a balloon expandable endoprosthesis but more preferably is a self-expanding prosthesis. The endoprosthesis is enclosed within the constraining sheath which is an outer, disruptable, preferably implantable tubular sheath which is preferably made of porous expanded polytetrafluoroethylene (hereinafter ePTFE, made as generally taught by U.S. Pat. Nos. 3,953,566 and 4,187,390 to Gore). The constraining sheath is characterized by having means for disruption such as a row of perforations or a seamline, with disruption of the constraining sheath and release of the endoprosthesis (resulting in expansion and deployment of the endoprosthesis) initiated by a distending force applied to the containment sheath. Preferably, disruption of the constraining sheath entails interruption of the continuity of the circumference of the constraining sheath, for example, as by tearing of a row of perforations.
The constraining sheath and endoprosthesis are mounted together as an assembly on an angioplasty balloon for delivery. Preferably, deployment of the endoprosthesis entails inflating the angioplasty balloon to a pressure sufficient to disrupt or break the constraining sheath in a prescribed fashion, thereby allowing a self-expanding endoprosthesis to spontaneously deploy. The catheter balloon thus supplies the necessary distending force to initiate disruption of the constraining sheath.
The constraining sheath is preferably attached to the endoprosthesis and is implanted along with the device. In this fashion, a self-expanding endoprosthesis can be deployed using methodologies and procedural techniques identical to those routinely employed for the implantation of balloon-expandable endoprostheses.
A self-expanding endoprosthesis can also be used to advantage to provide the necessary distending force (i.e., without requirement for a catheter balloon) if an alternative mechanism is supplied to enable disruption of the constraining sheath. Additionally, if a balloon is employed, the balloon""s inflated diameter under at least a length of the self-expanding endoprosthesis may be smaller than the intended deployed diameter of the endoprosthesis, yet large enough to initiate disruption or breaking of the constraint.
The phrase xe2x80x9cstent graftxe2x80x9d is used herein to describe a stent provided with a covering, typically of a vascular graft material such as ePTFE or polyethylene terephthalate. The covering may be provided over either or both of the inner and outer surfaces of the stent. The covering may cover a portion of the otherwise open stent interstices or it may cover all of the stent interstices.
With regard to either a self-expanding or a balloon expandable endoprosthesis, the constraining sheath may be employed to provide a smoother and more lubricious exterior surface during delivery than would be possible with a balloon expandable stent that would otherwise present a relatively rough exterior surface to the lumen of the blood vessel into which it is inserted.
The breakaway constraining sheath of the present invention overcomes many of the disadvantages of the previously described delivery systems and establishes numerous unique advantages. The sheath of the present invention, particularly when made of ePTFE, has a much smoother, continuous outer surface than the fiber-based systems, which may reduce the incidence of iatrogenic endothelial traumatization. It may be used to deploy a device beginning at the tip end and progressing to the hub end (i.e., distal end to proximal end), or hub end to tip end, or both ends toward the middle, or middle to both ends. The constraining sheath when made of a preferred ePTFE material may be provided with an extremely thin wall thickness (adding only 0.025-0.050 mm to total introductory profile) while providing extremely high strength. This enables substantial diametrical compaction of the device. The ePTFE sheath can allow almost immediate tissue ingrowth due to its inherent porous microstructure and thereby assist in anchoring the endoprosthesis. The sheath can be affixed to the exterior of an endoprosthesis, or alternatively can be provided without direct attachment to the endoprosthesis.
The constraining sheath can be configured to secure the endoprosthesis to the underlying delivery system. This may be accomplished by releasably attaching portions of the constraining sheath to the dilatation balloon or to the dilatation balloon catheter.
The deployment mechanism mimics the procedural techniques used with popular balloon-expandable endoprostheses and thus will require minimal user training. The flexibility of the delivery system is minimally compromised, which is important for device delivery through tortuous anatomy. Reliability of deployment may be improved. There is a high degree of confidence in deployment reliability since this constraint is not compromised by subsequent stitching or the use of pull strings, rip-cords or deployment lines, creep of constraints, overcoming high static frictional forces, etc. Since the sheath is provided over an endoprosthesis mounted on the angioplasty balloon, this system affords the opportunity for xe2x80x9cprimary stenting,xe2x80x9d that is, device implantation without preceding balloon dilatation of the host vessel. If primary stenting proves feasible for the particular patient, fluoroscopy time may be reduced (reducing the exposure of both patient and clinician to x-ray), as well as overall procedural time and expense. Risk of emboli formation may also be reduced. Additionally, once implanted, the self-expanding device is completely unconstrained, thereby allowing for compensatory remodeling (i.e., continued enlargement of the endoprosthesis over time).
The present invention provides a method of manufacture for the constraining sheath, and also relates to its assembly over a balloon catheter and an endoprosthesis. It also provides a means of controlling the radial dynamics of device deployment. For example, the present invention can be configured to xe2x80x98popxe2x80x99 open to allow rapid device deployment, or alternatively to undergo more gradual, high strain yielding prior to disruption and device deployment, or a combination of both.
The present invention preferably includes one or more lines of perforations as a means to render the constraint disruptable in a prescribed fashion, the perforations being generally oriented along the longitudinal axis of the device. Alternative perforation patterns (e.g., helical, discontinuous, zigzag, etc.) are also possible.
Disruption of the inventive constraining sheath is possible via other methods, which typically involve creating a line or zone of weakness along the length of the sheath such as by the use of a lesser amount of material in the zone of weakness. Other methods of creating a zone of weakness may include the application of thermal or mechanical treatments to a localized region. Additionally, active elements such as spring components or elastic segments included with the sheath may be used to facilitate constraining sheath removal.
Embodiments of the present invention also allow removal of the external constraining sheath, following disruption, along with the delivery catheter. This may be accomplished by securing the hub or proximal end of the constraining sheath to the catheter and optionally providing the sheath with several parallel perforated seams.
The constraining sheath may be imbibed with various pharmaceutical, biological, or genetic therapies for targeted luminal delivery of these substances. Following deployment of the endoprosthesis, these therapeutic agents can be released over time. An advantage of this approach is that the loading of the sheath with any of these therapeutic agents can be performed independent of the endoprosthesis manufacture. Further, radiopaque elements may be incorporated into the constraining sheath to facilitate fluoroscopic visualization.
The present invention may also be used to deliver and deploy multiple, coaxially loaded devices.
The present invention preferably employs a balloon with a shorter inflated working length than that of the endoprosthesis. This configuration allows full deployment of the self-expanding endoprosthesis with the ability to dilate the mid-length of the endoprosthesis in one step. The shorter length balloon minimizes the risk of dilating healthy vessel tissue adjacent to the deployed endoprosthesis.
In a preferred embodiment, the constraining sheath can be made to be extremely thin, or xe2x80x9cdelicate,xe2x80x9d for minimal implantation profile. Such a delicate constraining sheath is not adequate, without further exterior support, to constrain the endoprosthesis assembly (particularly when the assembly includes a self-expanding endoprosthesis) for very long periods of time or for shorter periods when exposed to elevated temperatures. The use of such a delicate constraining sheath is made practically possible when the assembly is provided with an additional packaging sheath that prevents inadvertent disruption of the constraining sheath or undesirable increase in diameter of the assembly (in an amount of 0.15 mm or more). The packaging sheath is removed prior to implantation and accordingly is not required to be made of an implantable material or a material with a thin wall. Alternatively, the endoprosthesis assembly may incorporate such a delicate constraining sheath if it is stored at reduced temperatures, such as 5xc2x0 C. or less, prior to implantation.